Happy Singles Day

Happy Time Limit for Singles Day: 1000 MS | memory limit: 65535 KB difficulty: 2

Description

Today is Singles Day. Smart NS comes up with an activity to enrich this Singles Day.

The rules are as follows:

Each bachelor writes a name of the girl you like on a piece of paper, and then loads the paper into a box. These sticks extract one piece of paper in sequence. If the name above is the girl you like, then the host called the girl at the scene to tell her the affection of the bachelor, and let the bachelor confess on the spot and get the blessing of everyone on the scene, you will be spared.

Suppose there are a total of N bachelors, m of which have not drawn their own paper, and how many possibilities are there for this situation ..

Input

Each row contains two integers, N and M (1 <m <= n <= 20), ending with EOF.

Output

For each test instance, please output a total number of possibilities for this situation, each instance's output occupies a line.

Sample Input

2 23 2

Sample output

13

Happy Singles Day